Method of treating animal and vegetable oils



Patented Mar. 1, 1949 METHOD OF TREATING ANIMAL AND VEGETABLE OILSFrederick C. Bersworth, Verona, N. J.

No Drawing. Application March 17, 1948, Serial No. 15,515

11 Claims.

This invention relates to chemistry, and more particularly to organicchemistry, and-has for its object the provision of a method of treatinganimal and vegetable oils to remove therefrom associated inorganicimpurities and freefatty' acids and to recover the fatty acid andglycerine contents thereof in a high state of purity.

Another object is to provide a method of producing fatty acid glycerinecompounds substantially free of associated inorganic impurities and offree fatty acids.

Still another object is to provide an improved process for formingsubstantially pure free fatty acids.

Other objects will be apparent as the invention is more fullyhereinafter disclosed.

It is well known in the art that animal and vegetable oils containvarious inorganic impurities, and free fatty acids, the amount and kindthereof varying widely depending upon the origin and history of the oiland the extent to which the oil has been refined and purified as well asthe care with which the oil has been refined, shipped and handled. Noprocess is known today by which the inorganic impurities contained inthe oil can be substantially completely removed from such oils,particularly those not susceptible to separation by such physical meansas distillation and filtering. The present invention aims to providesuch a process.

I have discovered that by treating such oils with an aqueous solutioncontaining the di-alkali metal salt of ethylene diamine tetraaceticacid, the major portion of the basic inorganic compounds present in theoil are solubilized as poly-metallic salts and complexes of this aminoacid and that these poly-metallic salts are highly reactive in theirionized state in aqueous solution as sequestering agents for otherneutral inorganic salts present in the oil forming water solublecomplexes therewith of unknown composition.

Most animal and vegetable oils consist mainly of fatty acid glyceridecompounds. Some oils,

however, either originally or following one or.

more refining steps contain some free fatty acids which in contact withmetal surfaces or with basic metal compounds react therewith to formmetallic soap compounds which are miscible or soluble in the fatty acidglycerides. Further, some oils are subjected to refining operations inwhich metallic catalysts are employed with the result that certainamounts of this catalyst contaminate the oil either in the form ofsubmicroscopic suspended particles or as metallo-organic compoundsdissolved in the glycerides.

The di-alkali metal salt of ethylene diamine tetraacetic acid, inaqueous solution has an alkaline pH of about 8 but due tothe presencetherein of two acid carboxylic groups the salt reacts chemicall in suchalkaline pH solutions as a strong acid towards metals and basic metalcompounds, such as oxides, hydroxides and carbonates, formingpoly-metallic tetra salts which are highly soluble in water.

In the treatment of animal and vegetable oils with the di-alkali metalsalt of ethylene diamine tetra-acetic acid to remove therefrom theassociated inorganic impurities, the practice may be modified widelywithout essential departure from the invention depending upon Whetherthe purified oil only is desired or the purified, fatty acidfree oil isdesired, or upon whether it is desired to decompose the oil into fattyacid and glycerine components, each being substantially free fromassociated inorganic impurities.

As one specific example of the present invention the practice ofremoving the associated inorganic impurities only will first bedescribed. In this process the oil is agitated with an aqueous solutioncontaining from 2% to 10% of the dialkali metal salt of ethylene diaminetetra-acetic acid, for example, the di-sodium salt of this amino acid.The relative volumes of oil and solution may be varied widely withoutessential departure from the invention as long as the disodium saltcontent of the solution is sufiicient in amount to react with themetallic and basic compounds present in the oil to form poly-metal tetrasalts therewith. In the absence of such basic metal compounds and in thepresence of associated non-basic inorganic salts, such as chlorides,sulfates, etc., it is sometimes advantageous to add to the agitatedoil-water solution a sufficient amount of some basic compound such asalkaline earth metal oxide, hydroxide or carbonate to form at least asmall amount of the poly-metal tetra salt by reaction of the alkalineearth metal oxide with the (ii-alkali metal salt thereby to sequesterthese electrolytes in aqueous solution as Water soluble complexes.

Generally, a volume ratio of /2' to 1 of aqueous di-alkali metal saltsolution to oil is adequate with good agitation to obtain a gooddispersion of the oil in water or vice versa, and to remove from the oilthe associated inorganic impurities, where the concentration of thedi-alkali metal amino acid salt in the solution is as low as 5%. Heatingof the agitated oil-water mixture facilitates the chemical reactionsinvolved but temperatures in excess of the vaporizing temperature ofeither component of the mixture should. be avoided.

After thorough agitation of the oil-aqueous solution mixture for anextended time interval effective to complete the chemical reactionsinvolved and to attain chemical equilibrium conditions, the mixture isallowed to cool and settle into water and oil fractions which areseparated from each other in any convenient manner.

The aqueous solution fraction after being evaporated to a volumeproviding a concentrated solution of the poly-metallic salt of ethylenediamine tetra-acetic acid is acidified with a strong mineral acid (HClor H2SO4) to a pH of about 1.2 to precipitate out the insolubletetraacetic amino acid which is recovered and redissolved in causticalkali solution for re-use as the di-alkali metal salt in the treatmentof additional quantities of oil. The filtrate from the acidprecipitation step normally is discarded.

Many tests have shown that the animal and Vegetable oil fractionobtained is substantially completely free of associated inorganicimpurities, and that the only metallic or metalloid constituentsremaining therein are those bound chemically in non-reactive organicgroups present in the oil which normally cannot be expected to beremoved under the reaction conditions involved.

In this invention the di-alkali metal salt of ethylene diaminetetra-acetic acid may be comprised of any one of the alkali metals,sodium, potassium, lithium or caesium. The di-sodium salt is the leastexpensive and most economically practical salt to employ, although forcertain purposes some of the other di-alkali metal salts are betterreactants.

Animal and vegetable oils treated in accordance with the first examplemay contain some free fatty acids or metallic fatty acid soap compoundswhich are non-reactive with the di-alkali metal ethylene diaminetetra-acetic acid under the conditions given in the example. Theaddition of free alkali to the agitated oil-amino acid salt solutionmixture of the first example in an amount calculated to be approximatelysufficient to neutralize the free fatty acid content of the oil and. todecompose by base exchange reaction the metallic soap compounds presentin the oil, will efiectively remove these two undesired impurities fromthe oil leaving on settling separation substantially pure fatty acidglycerides with the alkali metal-fatty acid soap compounds dissolvedalong with the amino acid salts in the aqueous fraction.

Alternatively, the alkali metal hydroxide solution may be added first tothe agitated oil and the free fatty acids present therein saponified tofatty acid soap compounds prior to the addition of the di-alkali metalamino acid salt solution. A third alternative is to form an aqueoussolution of the di-alkali metal salt and an alkali metal hydroxide inwhich the alkali metal hydroxide approximates one molar weight per molarweight of the di-alkali metal salt. In such a solution the amino acidsalt present consists essentially of the tri-alkali metal mono-acidsalt. In such an amino acid salt the third alkali metal ion whichneutralizes one of the secondary carboxylic acid groups is available forbase exchange reaction with the free fatty acids and with the metallicsoap compounds of the oil. The alkali metal ions neutralizing theprimary carboxylic groups are not open to base exchange reaction.

The fatty acid soap compounds thus formed in the oil are soluble in theaqueous solution and may be recovered therefrom after separation of theoil and water fractions by acidification to a pH at which the fatty acidsoaps are decomposed generally at a pH of about 4.5, freeing the fattyacid from alkali metal combination. The insoluble fatty acid isseparated from the acid aqueous solution and on further acidification ofthe solution to a pH of 1.2 the amino acid is precipitated andrecovered, as hereinabove disclosed.

Where, as in the third modification of this invention, it is desired toconvert the oil into fatty acid soap compounds and glycerine directlywithout first removing the assosciated inorganic impurities or metallicfatty acid soaps as above described, the oil may be saponified inaccordance with prior art practices using a caustic alkali solution suchas NaOH in which is dissolved ethylene diamine tetra-acetic acid, theamount of said solution used being limited to that which providesapproximately enough alkali metal ions to neutralize the fatty acidspresent in a known quantity of the oil plus not less than 2 and not morethan 3 molar weights of caustic alkali per molar weight of ethylenediamine present in the solution. By so limiting the quantities ofreactants during saponification a final saponified reaction product isobtained which on attaining chemical equilibrium contains sufficientdi-alkali metal salt of ethylene diamine tetra-acetic acid to react withsubstantially all basic metallic compounds set free during thesaponification reaction to form poly-metal tetra salt compounds ofethylene diamine tetra-acetic acid which are active as sequesteringagents for neutral inorganic salts and compounds present therein.

The precise amount of ethylene diamine tetraacetic acid to any givenvolume of caustic alkali solution in this modification may vary widelywithout essential departure from the invention as long as the ratios ofalkali metal hydroxide to amino acid expressed above are maintained inthe saponification reaction. An amount of the tetra-acid approximating5% generally has been found to be adequate. Any amino acid in excess ofthat required for reaction with basic metal compounds is recoverablesubsequently for re-use in the process as hereinabove indicated. Aslight excess of caustic alkali over that required for saponificationnormally is desirable.

In the practice of this modification, an alterna tive practice is tosaponify the oil with an aqueous solution containing ethylene diaminetetra-acetic acid and alkali metal hydroxide in the ratio of 1 molarweight of the diamine to three molar weights of the hydroxide whichprovides an aqueous solution of the tri-alkali metal salt of ethylenediamine tetra-acetic acid. This salt, per se, is a strong sanopifyingagent for fatty acid glycerides giving up to the fatty acid the alkalimetal ion neutralizing one of the secondary carboxylic groups presenttherein and forming the di-alkali metal salt of the tetra-amino acid.

The tetra alkali metal salt of ethylene diamine tetra-acetic acid alsois, per se, a saponifying agent for fatty acid glyceride compoundsgiving up to the fatty acid both alkali metal ions neutralizing the twosecondary carboxylic groups present therein being converted thereby intothe di-alkali metal salt of the tetra-amino acid.

Whereas, the triand tetra-alkali metal salts of ethylene diaminetetra-acetic acid may be used as a saponifying agent by employing anaqueous solution of the salts containing one molar weight of the saltfor each oneand each two molar Weights, respectively, of fatty acidspresent in the oil, the use of a caustic alkali solution containingcaustic alkali and about ethylene diamine tetra-acetic acid (as thetetra-alkali metal salt) in the approximate amount providing uponsaponification of the oil an alkali metal hydroxide content not inexcess of about two molar weights per molar weight of the diamine ofthat required to neutralize all of the fatty acids present in the oil,is preferred for economic reasons and for the subsequent ease inprocessing the aqueous solution for the recovery of the amino acidcontent thereof as the free amino acid for re-use in the process.

Following saponification of the oil for the complete conversion of thefatty acid content thereof to fatty acid soap compounds, the fattyacid-soap compounds obtained are dissolved in hot water and sodiumchloride in an amount sufficient to insolubilize the soap compounds isadded to the soap solution. The insolubilized soap compounds areseparated from the aqueous solution and the water of the solution isremoved by evaporation to a concentration effective to precipitate themajor portion and substantially all of the sodium chloride from theconcentrated solution.

The sodium chloride-free aqueous solution remaining is separated fromthe precipitated chloride and is acidified, preferably with HCl, to a pHof about 1.2 to precipitate the ethylene diamine tetra-acetic acidcontent thereof which is recovered by filtration and the acid solutionremaining is neutralized, preferably by caustic alkali, the glycerinecontent of the solution being recovered therefrom by distillationmethods, well known in the art.

As will be recognized, it is preferable to employ the lowest practicalamount of ethylene diamine tetra-acetic acid effective to remove theassociated metallic impurities in the practice of this modification ofthe present invention in order to economize and to facilitate therecovery of the same as the free amino acid during processing of thesolutions after saponification.

Where it is desired to produce free fatty acids from the fatty acid soapcompounds produced in accordance with the above disclosures, the fattyacid soap compounds after separation from the aqueous solution, as abovedescribed, are redissolved in water and the soap solution obtained isneutralized with a strong mineral acid to a pH of about 4.5 toinsolubilize the free fatty acids. Only those fatty acids which areinsoluble in water may be recovered in this manner.

It is believed apparent from the above disclosure that the invention maybe widely modified without essential departure therefrom and all suchmodifications and departures are contemplated as may fall within thescope of the following claims,

What I claim is:

1. The method of treating animal and vegetable oils to free the samefrom metallic impurities which comprises agitating the said oil with anaqueous solution containing-an alkali metal salt of ethylene diaminetetra-acetic acid having at least two and not over three of itscarboxylic groups neutralized by an alkali metal ion.

2. The method of claim 1, wherein the said salt is the di-alkali metalsalt of ethylene diamine tetra-acetic acid and the amount thereof isapproximately that providing from about 2 to'10% of the salt in theaqueous solution.

3. The method of claim 1, wherein the said aqueous solution containsalkali metal hydroxide and ethylene diamine tetra-acetic acid in therela- Q weights per molar weight of ethylene diamine tetra-acetic acidpresent therein.

4. The method of claim 1, wherein aqueous solution contains an alkalimetal hydroxide and ethylene diamine tetra-acetic acid, each in suchrelative amounts providing an'amount of alkali metal hydroxidesubstantially sufficient to saponify the entire fatty acid content of aknown volume of said oil and an amount of alkali metal hydroxide inexcess thereof substantially equivalent to two molar weights per molarweight of ethylene diamine tetra-acetic acid present therein. 5. Themethod of claim 1, wherein said aqueous solution contains an alkalimetal hydroxide and ethylene diamine tetra-acetic acid in the relativeproportions of at least two molar weights of the hydroxide'to each molarweight of the tetra-acid and up to a maximum of not over 2 molar weightsof the hydroxide per molar weight of the tetraacid in excess of thatmolar weight empirically required to substantially completely neutralizethe fatty acid content of a known quantity of the said oil.

6. The method of treating animal and vegetable oils to remove therefromassociated metallic and basic metal compounds and inorganic saltimpurities which comprises agitating a known volume of the oil with anaqueous solution containing from 2 to 10% of a di-alkali metal salt ofethylene diamine tetra-acetic acid, the relative volumes of the oil andwater being that providing good emulsification of one into the other.

7. The method. of treating animal and vegetable oils to remove therefromthe free fatty acid content thereof and associated inorganic impuritieswhich comprises agitating a. known volume of the oil with an aqueoussolution containing an alkali metal hydroxide and ethylene diaminetetra-acetic acid, the amount of said hydroxide in the solution beingthat empirically sufiicient to react with the fatty acid content of theoil and with not less than two and not over three carboxylic groups ofthe known quantity of tetra acid present in the solution, the saidaqueous solution containing about 5% of said tetra acid.

8. A treating agent for animal and vegetable oils, said agent consistingof an aqueous solution containing an alkali metal hydroxide and ethylenediamine tetra-acetic acid in the relative amounts providing a. minimumratio of two molar weights of the hydroxide for each molar weight of thetetra acid up to a maximum ratio providing an amount of said hydroxidein excess of this minimum amount sufiicient to substantially completelysaponify the fatty acid content of a known volume of the oil.

9. The method of processing animal and vegetable oils to recovertherefrom the fatty acid glyceride content substantially free of freefatty acids and associated inorganic impurities which comprisesagitating the oil while in its liquid phase with an aqueous solutioncontaining an alkali metal hydroxide and ethylene diamine tetraaceticacid, the hydroxide content of said solution being substantially thatproviding an amount of hydroxide empirically equivalent to the freefatty acid content of the said oil, plus an amount approximating twomolar weights per molar maaeaozis weighttof tetra acid present in thesolution and the amount of the tetra acid present being within the rangeof 2% to 10% based on the volume of the said solution, and separatingthe oil and water mixture obtained to recover the glycericle compoundstherefrom.

10. The method of processing animal and vege table oils which comprisessaponifying the oil with an aqueous solution containing an alkalinemetal hydroxide and ethylene diamine tetra-acetic acid,

the amount of hydroxide present in the solution being approximately thatproviding an excess over that required to substantially completelysaponify the fatty acid content of a known volume of the oil which isnot less than two molar weights and not over three molar Weightsequivalent to the known amount of ethylene diamine tetra-acetic acidpresent therein, dissolving the fatty acid soap compounds formed inwatenvadding sodium chloride to the resultant solution to insolubilizethe fatty acid soap compounds present therein and separating the samefrom the solution, removing the water from the solution down to thepoint where the major portion of the sodium; chloride precipitatestherefrom and separating said chloride from the solution,

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,164,012 'Hund et al. June 27,1939

